• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.139.1-139.1
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• 2012

Wilson and Bappu (1957) found a significant relationship (WBR) between the absolute magnitude ($M_v$) and the width of the Ca II K emission line (W) for late type stars. In this study, we revisit the WBR to claim that WBR can be an excellent indicator of stellar surface gravity. We analyze 95 high-resolution spectra of G, K and M type stars obtained with UVES and BOES. WBR found in this work is $M_v$=34.22-18.34logW. In addition, stellar atmospheric parameters ($T_{eff}$, logg, [Fe/H], ${\xi}_{tur}$) are determined with the MOOG code and the Kurucz ATLAS9 model grids for G and K type stars. For M type stars, the method of Belle et al. (1999) is used to derive effective temperature which shows good agreement with other methods. Using the derived $T_{eff}$ and the measured logW,we find the relationship between logg and [logW, logT]; ${\log}g-_{fit}=-25.051-5.527{\log}W+10.254{\log}T_{eff}$. This relation can be applied to estimate the surface gravity of M type stars, which is difficult to be determined by other methods.

• Journal of the Korean Chemical Society
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• v.34 no.1
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• pp.91-97
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• 1990

Copolymers (PSAA) of styrene-acrylic acid were prepared through a free radical mechanism using azobisisobutyronitrile as an initiator. The fluorescence emission spectra of PSAA and the styrene-acrylic acid copolymers complexed with $Eu^{3+}$ (PSAA-Eu) were studied. The excimer fluorescence, centered at 330 nm, increases when the styrene mole fraction increases. Since the excimer fluorescence intensities of PSAA-EU, PSAA-Tb and PSAA-Eu-Tb were almost same, it appears that the kind of metal ion does not affect the excimer fluorescence. An interpretation of the results which takes into account the statistical composition of the copolymers, indicates that energy migration can occur from isolated to non-isolated styrene units.

• Bulletin of the Korean Chemical Society
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• v.25 no.1
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• pp.51-54
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• 2004

Gallium nitride (GaN) powders were prepared by calcining a gallium(III) nitrate salt in flowing ammonia in the temperature ranging from 500 to 1050 $^{\circ}C$. The process of conversion of the salt to GaN was monitored by X-ray diffraction and $^{71}Ga$ MAS (magic-angle spinning) NMR spectroscopy. The salt decomposed to ${\gamma}-Ga_2O_3$ and then converted to GaN without ${\gamma}-{\beta}Ga_2O_3$ phase transition. It is most likely that the conversion of ${\gamma}-Ga_2O_3$ to GaN does not proceed through $Ga_2O$ but stepwise via amorphous gallium oxynitride ($GaO_xN_y$) as intermediates. The GaN nanowires and microcrystals were obtained by calcining the pellet containing a mixture of ${\gamma}-Ga_2O_3$ and carbon in flowing ammonia at 900 $^{\circ}C$ for 15 h. The growth of the nanowire might be explained by the vapor-solid (VS) mechanism in a confined reactor. Room-temperature photoluminescence spectra of as-synthesized GaN powders obtained showed the emission peak at 363 nm.

• Journal of the Korean Vacuum Society
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• v.21 no.4
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• pp.212-218
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• 2012

The optical properties of AZO thin films prepared by the RF mangnetron sputtering system was studied to research the dependance of chemical properties of substrate. The substrate was the SiOC film deposited by Inductively coupled plasma chemical vapor deposition with various gas flow rate of $O_2$ and Ar (DMDMOS). In accordance with the increase of Ar gas flow rates, the Si-O bond in the SiOC film increased and then progressed the amorphism. The roughness of AZO grown on SiOC film with high degree of amorphism decreased and then improved the flatness of surfaces. Moreover, the ultra violet emission with high intensity was spontaneously induced in the AZO film growed on SiOC film with high degree of amorphism.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.9
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• pp.760-765
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• 2011

Znic sulfide (ZnS) thin films were deposited on glass substrates by radio frequency magnetron sputtering. The substrate temperature varied from room temperature (RT) to $500^{\circ}C$. The structural and optical properties of ZnS films were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive analysis of X-ray (EDAX) and UV-visible transmission spectra. The XRD analyses reveal that ZnS films have cubic structures with (111) preferential orientation, whereas the diffraction patterns sharpen with the increase in substrate temperatures. The FESEM images indicate that ZnS films deposited at $400^{\circ}C$ have nano-sized grains with a grain size of ~ 67 nm. Then films exhibit relatively high transmittance of 80% in the visible region, with an energy band gap of 3.71 eV. One obvious result is that the energy band gap of the film increases with increasing the substrate temperatures.

• Journal of Sensor Science and Technology
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• v.19 no.6
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• pp.428-434
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• 2010

In this study, a novel gas sensor based on evanescent field coupling between single mode side polished fiber and solvatochromic dye dispersed polymer waveguide was demonstrated. We fabricated a side polished optical fiber device as a volatile organic compounds gas detector. Solvatochromic dye was coated on the top of the side polished optical fiber to take advantage of evanescent field coupling. The solvatochromism can be defined as the phenomenon whereby a compound changes color, either by a change in the absorption or emission spectra of molecule, when reacted in different VOCs. The device reacted to polarity gases like a hexane, butane, xylene etc. The resonance wavelength was shifted by the xylene concentration which range was 0.1 ppm ~ 100 ppm. Also, the response with the concentration was lineer and the detection limit was 0.1 ppb.

• Journal of Astronomy and Space Sciences
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• v.33 no.4
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• pp.247-256
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• 2016

An analysis of light curves and spectra of observed gamma-ray bursts in gamma-ray ranges is frequently demanded because the prompt emission contains immediate details regarding the central engine of gamma-ray bursts (GRBs). We have revisited the relationship between the collimation-corrected peak luminosity and the spectral lag, investigating the lag-luminosity relationships in great detail by focusing on spectral lags resulting from all possible combinations of channels. Firstly, we compiled the opening angle data and demonstrated that the distribution of opening angles of 205 long GRBs is represented by a double Gaussian function having maxima at ~ 0.1 and ~ 0.3 radians. We confirmed that the peak luminosity and the spectral lag are anti-correlated, both in the observer frame and in the source frame. We found that, in agreement with our previous conclusion, the correlation coefficient improves significantly in the source frame. It should be noted that spectral lags involving channel 2 (25-50 keV) yield high correlation coefficients, where Swift/Burst Alert Telescope (BAT) has four energy channels (channel 1: 15-25 keV, channel 2: 25-50 keV, channel 3: 50-100 keV, channel 4: 100-200 keV). We also found that peak luminosity is positively correlated with peak energy.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.440-441
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• 2007

For this study, terbium-doped yttrium aluminum garnet (YAG:Tb) phosphor powders were prepared via the combustion process using the varous reagents. The characteristics of the synthesized nano powder were investigated by means of X-ray diffraction (XRD), Scanning Electron Microscope(SEM), and photoluminescence (PL). Single-phase cubic YAG:Tb crystalline powder was obtained at $1000^{\circ}C$ by directly crystallizing it from amorphous materials, as determined by XRD techniques. The SEM image showed that the resulting YAG:Tb powders had uniform sizes and good homogeneity. The photoluminescence spectra of the YAG:Tb nanoparticles were investigated to determinethe energy level of electron transition related to luminescence processes. There were three peaks in the excited spectrum, and the major one was a broad band of around 274 nm. Also, the YAG:Tb nanoparticles showed two emission peaks in the range of 450~500 nm and 525~560 nm, respectively, and had maximum intensity at 545 nm.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.3
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• pp.221-226
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• 2013

The water soluble quantum dots (QDs) are synthesized by the phase transfer and silica coating reaction. The photoluminescence intensity of silica-coated QDs are mainly affected by the amount of phase transfer agent, SDS (sodium dodecyl sulfate), and the maximum value is obtained at the cmc (critical micell concentration) concentration of SDS in the phase transfer reaction. Based on fluorescence spectra and field emission transmission electron microscope (FETEM), the energy transfer rate by forster resonance energy transfer (FRET) is increasing with the thickness of the silica shell coated on CdSe/ZnS QDs.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.413-416
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• 2004

In this study, zinc oxide(ZnO) having large misfit(18.2%) with sapphire was tried to be grown on very thin nitride buffer layers. For the creation of various kinds of nitride buffer layer, sapphire surface was modified by an irradiation of nitrogen ion beam with low energy generated from stationary plasma thruster(SPT) at room temperature. After the irradiation of ion beam, Al-N and Al-O-N bonding was identified to be formed as nitride buffet layers. Surface morphology was measured by AFM and then ZnO growth was followed by pulsed laser deposition(PLD). Their properties are analyzed by XRD, AFM, TEM, and PL. We observed that surface morphology was improved and deep level emission related to defects was almost vanished in PL spectra from the ZnO grown on nitride buffer layer.